An existing network in the mobile packet domain has a structure as illustrated in FIG. 1. As shown, a Gateway GPRS Supporting Node (GGSN), which is a gateway between a mobile communication network and an IP network, is responsible for assigning an IP address to a User Equipment (UE) to enable the UE to access the IP network; a Serving GPRS Supporting Node (SGSN) responsible for resource management and control is used to select an appropriate GGSN for the UE and provide a channel for communication between the UE and the GGSN; and a Home Location Register/Home Subscription Storage (HLR/HSS) is responsible for storing user subscription data.
As illustrated in FIG. 2, starting from the 3GPP R7, it is allowed to directly transfer user plane data between a radio network and a GGSN, but a connection in the signaling plane with the radio network is established through an SGSN, which is referred to as the One Tunnel architecture.
The 3GPP is under ongoing standardization efforts to simplify the structure of the network in the mobile packet domain, and FIGS. 3 and 4 are two promising future structures of the network in the mobile packet domain. As shown in FIGS. 3 and 4, a Packet Data Network Gateway (PDN GW) and a Serving Gateway (Serving GW) evolve from the GGSN, the PDN GW is responsible for assigning an IP address to a UE, and the Serving GW facilitates enabling the UE to move in a large range while maintaining the PDN GW unchanged; and a Mobility Management Entity (MME), which evolves from the SGSN, is responsible for resource management and control and selects an appropriate PDN GW for the UE.
As can be apparent from the foregoing descriptions, three logic nodes, i.e., a gateway node, a gateway selection execution node and a user subscription data storage node, with their relationships as illustrated in FIG. 5, exist in any of the existing network architecture in the mobile packet domain, the network architecture in the mobile packet domain defined in the 3GPP R7 and possible future network architectures in the mobile packet domain.
For any of the existing network architecture in the mobile packet domain, the network architecture in the mobile packet domain defined in the 3GPP R7 and the possible future network architectures in the mobile packet domain, the user subscription data is issued to the gateway selection execution node through the user subscription data storage node when the user is attached to the network, the user subscription data is also issued to a new gateway selection execution node through the user subscription data storage node if the original gateway selection execution node is replaced by the new gateway selection node while the user is moving, and in the case of a change in the user subscription data, the changed user subscription data is also issued to the new gateway selection execution node through the user subscription data storage node. A flow of the issuing is as illustrated in FIG. 6.
For any of the existing network architecture in the mobile packet domain, the network architecture in the mobile packet domain defined in the 3GPP R7 and the possible future network architectures in the mobile packet domain, selection of a gateway in the packet domain is performed by a gateway selection execution node in a flow as illustrated in FIG. 7, which generally includes:                Operation 1: A User Equipment transmits a bearer setup request to the gateway selection execution node;        Operation 2: The gateway selection execution node creates a Domain Name Server (DNS) request message;        Operation 3: The gateway selection execution node transmits the DNS parse request to a DNS server;        Operation 4: The DNS server returns to the gateway selection execution node a DNS parse result after parsing;        Operation 5: The gateway selection execution node selects from the DNS parse result a gateway node as an access gateway for the bearer setup request.        
In the operation 2, typically the gateway selection execution node determines an Access Point Name (APN) for DNS parsing by appending a country code and a network code of the user contained in an IMSI field of the user subscription data to an APN indicated by the user. Thus, even if an APN indicated by a roaming user is the same as that indicated by a local user, an appropriate gateway node for the roaming user can also be addressed according to the country code and the network code (an operator generally expects that traffic of its own user roaming to another operator can be forwarded to its own network node for processing).
In the operation 3, the DNS server of an operator has to be configured with all combinations of roam APNs of another operator, as well as country codes and network codes possessed by the another operator, to support a roaming user from the another operator.
In the operation 1, if the APN indicated by the user is not presented explicitly in the bearer setup request message transmitted from the User Equipment, it is essentially indicated that the user expects to use a default APN, and thus in the operation 2 the gateway selection execution node uses the default APN configured in the user subscription data as the APN indicated by the user when creating the APNX for DNS parsing.
Prior to the operation 2, the gateway selection execution node may select a gateway node according to a certain field contained in the user subscription data and that contained in the bearer setup request message transmitted from the user, and in this case the operations 2, 3, 4 and 5 may be not necessary. For example, if the bearer setup request message transmitted from the user contains the IP address of a gateway node of which the user expects the use, and the use of the gateway node by the user is also allowed according to the user subscription data, then the gateway selection execution node may select the gateway node to serve the user.
In the operation 2, the gateway selection execution node may append other information according to the configuration of an operator, e.g., part of contents other than the country code and the network code in the International Mobile Subscriber Identity (IMSI), when creating the APNX for DNS parsing.
Following the operation 5, if no gateway node can be selected in the operation 5 due to the lack of the IP address of a gateway node or a list of IP addresses of gateway nodes in the DNS parse result, or if the IP address of the gateway node selected in the operation 5 is unreachable, then the gateway selection execution node can reject the bearer setup request of the user, select a gateway node (e.g., a default gateway node) according to the configuration of the operator or select a gateway node according to the information in the user subscription data (e.g., a default gateway node configured in the user subscription information), or recreate an APNX for DNS parsing and repeat the operations 3, 4 and 5 to parse the address of the gateway node.
As can be apparent from an analysis of the foregoing prior art, there are the following drawbacks in the prior art:
1) In the prior art, to enable the roaming user equipment to access its home operator's gateway node, the DNS server of the roam operator (i.e. the operator to which the user roams) has to be configured with an Access Point Name (APN), a country code, a network code and a corresponding gateway address of the home operator, so that the gateway selection execution node of the roam operator can retrieve the address of the gateway node of the home operator in the DNS parsing process, and if the DNS server of the roam operator has not been configured with any address information of an access gateway node of the home operator, or the same Access Point Name (APN) as the home access gateway exists in the roam DNS server without storing any country code and network code of the home operator, then it is impossible to select any gateway of the home operator for the User Equipment.
2) The gateway selection solution in the prior art is demanding for the configuration of DNS servers of respective operators in that an APN, a country code, a network code and a corresponding gateway address corresponding to an operator has to be configured in DNS servers of other operators. When the gateway address of an operator is changed or a new network code is added for the operator, the DNS servers of other operators have to be modified, thus making data update inconvenient.
3) For a DNS server of an operator, at least contents such as an APN, a country code, a network code and a corresponding gateway address corresponding to the operator have to be stored, and since the country code and the network code do not correspond uniquely to an operator, that is, the operator may be provided with plural network codes, the DNS server of the operator has to store contents separately under various country codes and different network codes, resulting in a significant waste in the storage cost of the DNS server of the operator.
4) The existing gateway selection solution is inflexible in the DNS parsing process due to the limitation of information stored at the DNS server of the roam operator, thus making it inconvenient for the home operator to deploy a roam service.